The size versus quantity debate over lowest cost per kg to LEO for rockets on the internet has been inconclusive. Space X has announced a desire to get into the super heavy rocket market, via the Falcon X and XX. Is Space X after the super heavy rocket market because the customer is interested in a super heavy, or is it because larger rockets offer a quicker reduction in cost, than mass production of a smaller rocket, like the Falcon 1?

Space X is after super heavy launcher because Elon Musk is after landing on Mars.

Current;y there doesn't seem to be a lot of market for anything more capable than Falcon Heavy. SpaceX's proposal (more of a concept really) of X and XX was at that time more about flexing muscles than anything else.

There may be a bit of 'if you build it they will come' = If SpaceX make a Falcon Heavy X or XX, perhaps someone will come up with a use for it?

I am more than sure that SpaceX is constantly sounding the market and as soon as they're convinced there's demand, the real work will start. The concepts of X and XX are part of it. It's like saying: 'See that? We could totally do this rocket for you. Think if you have something to put on top of it.'

IIRC, Elon Musk stated in an interview that the Falcon X and XX concepts where more like the dream of an individual propulsion engineer than really an official SpaceX project.

Maybe they will do that some time, maybe not. At the moment it seems _highly_ unlikely that they are working on something like this given the enormous amount of work with "smaller" (haha) rockets they have to dig through right now.

In an attempt to try to answer your question:I think as long as we are using expendable launchers there is probably some kind of "sweet spot" between size and quantity. Building HUUGE rockets is unbelievably expensive and they tend to have low flight rates, but simply mass producing rockets will not bring your costs down if individual components are too expensive.

That's why SpaceX approach with the Falcon 9 and Falcon Heavy is so clever. The most expensive parts are probably the engines, so mass producing them is the way to bring their costs down. Combining multiple first stages to create a Heavy lift increases production demand for those elements while at the same time being able to launch a lot of stuff at once to further reduce the $/kg ratio.

In fact that is soo clever, that SpaceX weren't the first to come up with this idea, it is the basis for the Delta IV Heavy and there are plans (currently on ice afaik) for a similar Atlas 5 HLV (in both cases minus the propellant cross-feed SpaceX intends to do).

In fact that is soo clever, that SpaceX weren't the first to come up with this idea, it is the basis for the Delta IV Heavy and there are plans (currently on ice afaik) for a similar Atlas 5 HLV (in both cases minus the propellant cross-feed SpaceX intends to do).

If ULA is so clever, why didn't they use their talent and expertise to design a rocket as low cost to orbit as the Falcon 9 Heavy? (I don't expect an answer to this)

a) before Elon Musk came a long and said "We can do this better! Since I have the money, I'll just try it myself!" there was absolutely no incentive for ULA to provide cheaper services. Initially Boeing and Lockheed Martin had been competitors for the EELV market, by forming the ULA joint venture they actually formed a monopoly.

b) Cost plus contracts!Government pays ULA a billion! Dollars a year just so that they can continue to provide the service, even if there isn't a single launch. Why? Because ULA is so expensive, that there is not a single non-governmental customer! (they all launch on Ariane 5 or with one of the Russian providers)

c) because Boeing and Lockheed Martin are both HUUUGE companies with a lot of spacelaunch "legacy"/heritage. I'm pretty sure they both lack the structural efficiencies to provide cost effective services, even if they have the technology to do so.

In fact that is soo clever, that SpaceX weren't the first to come up with this idea, it is the basis for the Delta IV Heavy and there are plans (currently on ice afaik) for a similar Atlas 5 HLV (in both cases minus the propellant cross-feed SpaceX intends to do).

If ULA is so clever, why didn't they use their talent and expertise to design a rocket as low cost to orbit as the Falcon 9 Heavy? (I don't expect an answer to this)

I'm sure they could design one. Whether with all the people they need to pay they could then run it at a cost similar to SpaceX I think is unlikely.

And to be honest, even if they could design one, I would put money on the implementation being more expensive that SpaceX, mainly because of the management by committee approach they are bound to use. SpaceX has Musk telling the team what to do. One person with the vision, and the capability to drive it through.